Therefore, further studies are needed to clarify the relationship between androgens and PDE5 gene expression in the corpus cavernosum, but it is well-established that TRT improves the effect of PDE5i treatment in patients with hypogonadism (see Synergic Effect of T Plus PDE5is in the Treatment of Erectile Dysfunction in Patients with LOH). The gene discussed is PDE5A; the disease is hypogonadism.